tessl/npm-fast-xml-parser

Validate XML, Parse XML, Build XML without C/C++ based libraries

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Overview

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Files

XML Validation

Name: tessl/npm-fast-xml-parser
Author: tessl

Fast validation of XML syntax and structure without the overhead of full parsing. The validation system checks for well-formed XML, proper tag nesting, attribute syntax, and other structural requirements.

Capabilities

XMLValidator.validate

Validates XML syntax and returns detailed error information including line and column numbers for any issues found.

/**
 * Validates XML syntax and structure
 * @param xmlData - XML content as string
 * @param options - Optional validation configuration
 * @returns true if valid, ValidationError object if invalid
 */
XMLValidator.validate(xmlData: string, options?: validationOptions): true | ValidationError;

Usage Examples:

import { XMLValidator } from "fast-xml-parser";

// Basic validation
const xmlString = "<root><item>value</item></root>";
const result = XMLValidator.validate(xmlString);

if (result === true) {
  console.log("XML is valid");
} else {
  console.log(`Invalid XML at line ${result.err.line}, column ${result.err.col}: ${result.err.msg}`);
}

// Validation with options
const optionsResult = XMLValidator.validate(xmlString, {
  allowBooleanAttributes: true,
  unpairedTags: ['br', 'hr', 'img']
});

Configuration Types

validationOptions

Configuration options for XML validation behavior.

interface validationOptions {
  /** Allow attributes without values (e.g., <input checked>) */
  allowBooleanAttributes?: boolean;
  
  /** List of tag names that don't require closing tags */
  unpairedTags?: string[];
}

Default values:

allowBooleanAttributes: false
unpairedTags: []

ValidationError

Error object returned when validation fails, containing detailed error information.

interface ValidationError {
  err: {
    /** Error code identifier */
    code: string;
    
    /** Human readable error message */
    msg: string;
    
    /** Line number where error occurred (1-based) */
    line: number;
    
    /** Column number where error occurred (1-based) */
    col: number;
  };
}

Common Validation Scenarios

Boolean Attributes

HTML-style attributes without values:

import { XMLValidator } from "fast-xml-parser";

// This will fail with default options
const htmlLike = '<input type="text" required>';

// Enable boolean attributes
const result = XMLValidator.validate(htmlLike, {
  allowBooleanAttributes: true
});

Self-Closing Tags

Tags that don't need closing tags (common in HTML):

import { XMLValidator } from "fast-xml-parser";

// This will fail with default options
const htmlContent = '<p>Hello<br>World</p>';

// Allow br as unpaired tag
const result = XMLValidator.validate(htmlContent, {
  unpairedTags: ['br', 'hr', 'img', 'input']
});

Error Handling

import { XMLValidator } from "fast-xml-parser";

function validateAndHandle(xmlString) {
  const result = XMLValidator.validate(xmlString);
  
  if (result !== true) {
    // Extract error details
    const { code, msg, line, col } = result.err;
    
    throw new Error(`XML Validation Error (${code}) at ${line}:${col} - ${msg}`);
  }
  
  return true;
}